It is well known that hydrogensilanes can be reacted with allyl chloride in the presence of platinum compounds or metallic platinum, which may be present as such or applied to various substrates, to form 3-chloropropyl-silanes. Such reactions are disclosed, for example, in German Patents 20 12 229 and 28 15 316. It is further known that in the reaction of allyl chloride with hydrogensilanes to form 3-chloropropyl-silanes a portion of the allyl chloride reacts with the hydrogensilane in a so-called beta-cleavage side reaction to form propylene and the chlorosilane corresponding to the particular hydrogensilane starting compound. For instance, in the reaction of allyl chloride with trichlorosilane, about 36 mol-% of the allyl chloride involved in the reaction is converted by beta-cleavage into propylene, accompanied by the formation of equivalent amounts of silicon tetrachloride. The extent of this side reaction can be controlled only to a limited degree. By means of special reaction management in a pressure apparatus the formation of propylene can be suppressed; however, this method of operation has as its consequence that the propylene which is formed due to the beta-cleavage further reacts quantitatively to form propyl-silanes which correspond to the hydrogensilane starting compounds. Even in the reactions performed under normal pressure in conventional manner, the propylene formed due to beta-cleavage reacts to a significant degree with hydrogensilane to form the corresponding propyl-silanes. Thus, for example, in a hetero-geneous-catalytic reaction of allyl chloride and trichlorosilane on a technical scale in a column filled with platinized activated charcoal, up to 230 kg of propyltrichlorosilane are obtained per 1000 kg of 3-chloropropyltrichlorosilane, which represents an excess requirement of about 28% of trichlorosilane, based on the amount of trichlorosilane incorporated into the target product.
Whereas the chlorosilanes which are formed in stoichiometric ratio with respect to the formation of propylene due to beta-cleavage, for example silicon tetrachloride when trichlorosilane is used as the hydrogensilane component, can be easily separated by distillation from the other components of the particular reaction mixture because of the large boiling point differences, the separation of the corresponding propylsilanes from the 3-chloropropyl-silane target products is only possible with the aid of the expenditure of large distillation energy. Moreover, for most propylsilanes, such as methylpropyldichlorosilane, ethypropyldichlorosilane and dimethylpropylchlorosilane, there are at this time no fields of application, so that they require cost-intensive disposal means.